The present invention relates to an information recording method for forming a record mark on an optical recording medium by the heat of an optical beam and an information recording apparatus therefor, and in particular, to a method and an apparatus for recording information by a mark edge recording method.
With the demand of increasing the informational density of optical recording media, a mark edge recording method has been used widely as a recording method in recent years. In the mark edge recording method, the edge of a record mark corresponds to xe2x80x9c1xe2x80x9d of binary informational data. This method is capable of recording information at a higher density than that of a mark position recording method, in which the presence and absence of a record mark correspond to xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d, respectively.
In order to realize high density recording on an optical recording medium, it is important to secure the precision of the recording control in addition to usage of the mark edge recording method. In Japanese Patent Application Laid-Open No. 3-22223 (1991), the present assignee has proposed a control method and an apparatus therefor in which a signal of laser light irradiation for forming one record mark is pulsed whereby the length and the amplitude of the series of pulses for the next mark is adjusted depending on the length of the mark non-formed portion (space). In this control method, the shape distortion in the trailing edge of a mark due to the influence of the heat of the preceding mark can be corrected. However, there have still been unsolved problems of the shape distortion in the leading edge of the mark and of the shift of edge position.
A method for resolving the problem of the positional shift of a formed mark has been proposed in Japanese Patent Application Laid-Open No. 6-84224 (1994). The method is a multi-pulse recording method in which the power of laser light for forming a mark is pulsed by modulating into three values while the power of laser light for forming spaces is modulated into two values, and in which the length of the series of pulses is adjusted depending on the mark length. In this method, the amount of heat supply of the preceding mark is adjusted depending on the length thereof, whereby the positional shift of the next mark formation is prevented. However, there has been a problem that the influence of heat caused by the length of the preceding space can not be avoided.
Further, a recording method and a recording apparatus for maintaining the constancy of the positional shift quantity of a record mark edge has been proposed in Japanese Patent Application Laid-Open No. 6-76401 (1994). In the method, the shorter preceding space causes the later timing of the next light emission, and the longer record mark causes the earlier timing of the light extinction. However, there has been a problem of incapability of recording compensation corresponding to various combinations of the mark length and the space length of a data signal.
FIG. 1 and FIG. 2 are timing charts showing a record waveform together with the data to be recorded in accordance with a prior art. FIG. 1 shows a multi-pulse record waveform in accordance with Japanese Patent Application Laid-Open No. 6-84224 (1994), where the power of laser light for forming marks is modulated into three values of Pa, Pw1, and Pw2, while the power of laser light for forming spaces is modulated into two values of Pa and Pr. The number of irradiated pulses sequentially increases correspondingly to record marks 2T, 3T, . . . , 8T of (1, 7) RLL modulation coding. The region from the rise point to the fall point of data to be recorded corresponds to a record mark. The timing of pulse termination of each record mark is earlier by xe2x80x9cT/2xe2x80x9d than the timing of the fall of data to be recorded. This comes from the consideration that the trailing edge of a record mark expands rearward due to the influence of heat.
In a magneto-optical disk having record marks formed by the record waveform shown in FIG. 1, the shift quantity was measured for the leading and trailing edges of the record marks. The measurement has shown a large shift quantity for short marks. Further, the measurement of random jitter for leading and trailing edges has shown the jitter of 11.2% for leading edges, 12.1% for trailing edges, and 11.7% in average. Both the jitters of leading and trailing edges exceed the jitter tolerance of 10%. It has been also found that the jitter substantially increases with decreasing shortest length of record marks. Here, in the measurement of random jitter, the standard deviation of the time difference between the edge of a record mark and the edge of a reference clock signal is detected and expressed by the ratio to the reference clock.
FIG. 2 shows a multi-pulse record waveform proposed by the present assignee. In this method, the power of laser light for forming marks is modulated into four values of Pa, Pw1, Pw2, and Pw3, while the power of laser light for forming spaces is modulated into two values of Pa and Pb. The number of pulses sequentially increases correspondingly to each record mark 2T, 3T, . . . , 8T of (1, 7) RLL modulation coding. The timing of pulse termination of each record mark is earlier than the timing of the fall of data to be recorded similarly to FIG. 1.
In a magneto-optical disk having record marks formed by such a record waveform, the shift quantity was measured for the leading and trailing edges of the record marks. The measurement has shown that the shift quantity is reduced in comparison with that by the record waveform shown in FIG. 1. That is, the measured random jitter for leading and trailing edges are 11.4% for leading edges, 10.5% for trailing edges, and 11.0% in average. The jitter of trailing edges is decreased in comparison with that by the record waveform shown in FIG. 1, however, the jitter values exceed the jitter tolerance.
As such, in the formation of record marks having various lengths such as 2T through 8T, there has been a limit in controlling the edge shift of each record mark only by adjusting the number of pulses and the power of laser. Further, the jitter substantially increases with decreasing shortest length of record marks. In particular, in a magnetic super-resolution medium capable of reproducing record marks having a dimension smaller than the beam spot, for example, a dimension of 0.4 xcexcm or less, there bas been a problem of a high jitter due to the positional shift of record marks.
The present invention has been devised considering such problems. An object of the invention is to provide an information recording apparatus and an information recording method in which the pulse start timing and/or the pulse termination timing of beam light are adjusted during the recording of those permutational combinations of a space of a predetermined length and a mark of a predetermined length, whereby the positional shift quantity of leading and trailing edges is reduced even for the marks having a dimension of 0.4 xcexcm or less, whereby the jitter is reduced.
The present assignee has obtained the following findings from the evaluation of edge shift for respective permutational combinations of spaces and marks recorded by the multi-pulse recording method described above (see FIG. 2). For the evaluation of edge shift, the edge shift quantity was measured for both the marks recorded in a pattern-shift pattern shown in FIG. 3A and the marks recorded in a thermal shift pattern shown in FIG. 3B. FIG. 3A and FIG. 3B are diagrams showing the record mark length and the space distance for the measurement of pattern shift and thermal shift. In the pattern-shift pattern, the space distance is kept constant and the record mark length is varied as shown in FIG. 3A. Using this pattern, the influence of the heat of record mark formation over the trailing edge of the record mark can be observed.
FIG. 4 is a graph showing the shift quantity in the length for each conventional mark recorded in the pattern-shift pattern. The (1, 7) RLL modulation code was used, and 2T through 8T marks were recorded on a magneto-optical disk capable of recording in both land and groove. The space distance was constant 8T. The axis of ordinate indicates the shift quantity (nsec.), and the axis of abscissa indicates the length of recorded marks (xc3x97T). In the measurement, the time corresponding to the formed length of a record mark is measured by a time interval analyzer, and the difference from the correct time of each record mark with the reference to the time of the shortest length mark is obtained as the shift quantity. That is, the shift quantity indicates the positional shift of a recorded mark from the correct position. Here, the shortest record mark is a 2T mark in case of (1, 7) RLL modulation code. The positive direction of the axis of ordinate indicates a longer mark, and the negative direction indicates a shorter mark.
FIG. 5 is a graph showing the shift quantity of leading and trailing edges for each conventional mark similarly recorded in the pattern-shift pattern. The axis of ordinate indicates the shift quantity (nsec.), and the axis of abscissa indicates the distance (channel clock length) between the leading edges of two consecutive marks or between the trailing edges of two consecutive marks. In the figure, the mark xe2x80x9cxcex94xe2x80x9d indicates that of leading edges, and the mark xe2x80x9cxe2x96xa1xe2x80x9d indicates that of trailing edges. The positive direction of the axis of ordinate indicates a forward shift quantity, and the negative direction indicates a rearward shift quantity.
FIG. 4 shows that 3T marks are shorter than the correct length. Further, FIG. 5 shows that the leading edges of 3T marks are in the correct position (that is, the shift quantity between the leading edges of 11T in the axis of abscissa is nearly zero). These facts show that the trailing edges of 3T marks are shifted forward. This implies that the heat is insufficient for forming 3T marks. The result is the same not only for the case of a constant space length of 8T but also for any case from 2T through 7T. That is, the trailing edges of 3T marks are shifted forward, and the length is shortened regardless of the preceding space length, which implies that the heat is insufficient for forming 3T marks.
Next, the shift quantity was evaluated for the spaces between record marks recorded by the thermal shift pattern. In the thermal shift pattern, the record mark length is kept constant, and the space distance is varied as shown in FIG. 3B. Using this pattern, the influence of the preheating in space distances over the leading edge of the next record mark can be observed. FIG. 6 is a graph showing the shift quantity of the space length between conventional marks recorded in the thermal shift pattern. The (1, 7) RLL modulation code was used, and constant marks with a space distance of 2T through 8T were recorded on a magneto-optical disk capable of recording in both land and groove. The mark length was constant 2T. The axis of ordinate indicates the shift quantity (nsec.), and the axis of abscissa indicates the length of recorded spaces (xc3x97T).
FIG. 7 is a graph showing the shift quantity of leading and trailing edges for each conventional mark similarly recorded in the thermal shift pattern. The axis of ordinate indicates the shift quantity (nsec.), and the axis of abscissa indicates the channel clock length between the leading edges of two consecutive marks or between the trailing edges of two consecutive marks. In the figure, the mark xe2x80x9cxcex94xe2x80x9d indicates that of leading edges, and the mark xe2x80x9cxe2x96xa1xe2x80x9d indicates that of trailing edges. The positive direction of the axis of ordinate indicates a forward shift quantity, and the negative direction indicates a rearward shift quantity.
FIG. 6 shows that 2T spaces are longer than the correct length. Further, FIG. 7 shows that the shift quantity between the leading edges at 5T in the axis of abscissa is shifted rearward, and FIG. 6 shows that the shift quantity of 3T spaces is nearly zero. These facts show that the leading edge of a mark following a 2T space is shifted rearward. This implies that the heat of preheating in 2T space portions is insufficient thereby causing the insufficiency of heat at the starting point of the next mark formation. The result is the same not only for the case of a constant mark length of 2T but also for any case of a record mark length from 3T through 8T. That is, the trailing edges of 2T spaces or the leading edges of the marks following a 2T space are shifted rearward regardless of the following mark length.
An information recording method in accordance with a first invention is characterized by comprising the following steps: determining the presence or absence of a permutational combination of a space of a predetermined length and a record mark of a predetermined length of inputted data to be recorded representing the record marks and the spaces to be formed; instructing to, when the determination result is the absence of said predetermined permutational combination, perform the start of the first pulse for forming the objective record mark at a start timing set correspondingly to the timing of switching to the record mark of said data to be recorded, and to perform the termination of the last pulse for forming said record mark at a termination timing set correspondingly to the timing of switching to the space of said data to be recorded; instructing, when the determination result is the presence of said predetermined permutational combination, timing the adjustment of advancing the start of the first pulse for forming a record mark of said predetermined length than said start timing and/or the adjustment of delaying the termination of the last pulse for forming the record mark of said predetermined length than said termination; and controlling the pulse timing of beam light from a light source in response to said instruction and thereby forming a record mark on said optical recording medium.
An information recording apparatus in accordance with a fourth invention is characterized by comprising: a determining unit for inputting data to be recorded representing the record marks and the spaces to be formed, and for determining the presence or absence of a permutational combination of a space of a predetermined length and a record mark of a predetermined length; an instructing unit for, when the determination result by said determining unit is the absence of said predetermined permutational combination, instructing to perform the start of the first pulse for forming the objective record mark at a start timing set correspondingly to the timing of switching to the record mark of said data to be recorded, and to perform the termination of the last pulse for forming said record mark at a termination timing set correspondingly to the timing of switching to the space of said data to be recorded; a timing adjustment instructing unit for, when the determination result by said determining unit is the presence of said predetermined permutational combination, instructing the adjustment of advancing the start of the first pulse for forming a record mark of said predetermined length than said start timing and/or the adjustment of delaying the termination of the last pulse for forming the record mark of said predetermined length than said termination timing; a light source capable of emitting pulsed beam light; and a beam light controlling unit for controlling the pulse timing of beam light from said light source in response to the instruction from said timing adjustment instructing unit.
In the first and the fourth inventions, when the data to be recorded contains a permutational combination of xe2x80x9cspace, record markxe2x80x9d previously expected to cause a large shift quantity, in order to reduce the shift quantity of the record mark, the start timing of pulse is advanced for a record mark the leading portion of which is expected to shift rearward, and the termination timing of pulse is delayed for a record mark the trailing portion of which is expected to shift forward, whereby the shift quantity is reduced and the jitter is reduced.
An information recording method in accordance with a second invention is characterized by a method of the first invention, wherein the presence or absence of said permutational combination including a shortest length space is determined in said determining step, and said method further comprising the step of instructing the adjustment of advancing the start of the first pulse for forming the objective record mark than said start timing when the determination result is the presence.
An information recording apparatus in accordance with a fifth invention is characterized by an apparatus of the fourth invention, said determining unit determines the presence or absence of said permutational combination including a shortest length space, and said timing adjustment instructing unit instructs the adjustment of advancing the start of the first pulse for forming the objective record mark than said start timing when the determination result by said determining unit is the presence.
In the second and the fifth inventions, when a record mark of any length is recorded after a shortest length space, the start of the first pulse for forming the record mark is advanced than said start timing. As described above, the present assignee has found that an nT record mark after a 2T space of the conventional (1, 7) RLL modulation code has a leading edge shifted rearward. Accordingly, the start of the first pulse of the objective record mark is advanced than the start timing of other record marks, whereby the shift quantity of record marks is reduced and the jitter is reduced.
An information recording method in accordance with a third invention is characterized by a method of the first or the second invention, wherein the presence or absence of said permutational combination including a record mark of a length requiring two pulses is determined in said determining step, and said method further comprising the step of instructing the adjustment of delaying the termination of the second pulse for forming the objective record mark than said termination timing when the determination result is the presence.
An information recording apparatus in accordance with a sixth invention is characterized by an apparatus of the fourth or the fifth invention, said determining unit determines the presence or absence of said permutational combination including a record mark of a length requiring two pulses, and said timing adjustment instructing unit instructs the adjustment of delaying the termination of the second pulse for forming the objective record mark than said termination timing when the determination result by said determining unit is the presence.
In the third and the sixth inventions, when a record mark requiring two pulses is recorded after a space of any length, the termination of the second pulse for forming the record mark is delayed than said termination timing. As described above, the present assignee has found that a 3T record mark after an nT space of the conventional (1, 7) RLL modulation code has a trailing edge shifted forward. Accordingly, the termination of the second pulse of the objective record mark is delayed than the termination timing of other record marks, whereby the shift quantity of record marks is reduced and the jitter is reduced.
An information recording apparatus in accordance with a seventh invention is characterized by an apparatus of the fifth invention, wherein said data to be recorded is (1, 7) RLL modulation code, and the shortest length space is a 2T space (where T is a unit period).
An information recording apparatus in accordance with an eighth invention is characterized by an apparatus of the sixth invention, wherein said data to be recorded is (1, 7) RLL modulation code, and the record mark of a length requiring two pulses is a 3T mark (where T is a unit period).
In the seventh and the eighth inventions, the information is recorded using (1, 7) RLL modulation code. The termination timing of the last pulse of a record mark (of any length) formed after a 2T space is delayed, whereby the jitter is reduced. Further, the start timing of the first pulse of a 3T mark following a space of any length is advanced, whereby the jitter is reduced.
An information recording apparatus in accordance with a ninth invention is characterized by an apparatus of any one of the fourth to the eighth inventions, wherein the start timing of said first pulse and the termination timing of said last pulse are set depending on a unit period defining the length of record marks and spaces to be formed, and the timing adjustment amount is set independently of said unit period.
In the ninth invention, the termination timing of the last pulse is set to be earlier, for example, by xe2x80x9cT/2xe2x80x9d, than the timing of switching of the data to be recorded, and the amount of timing adjustment of the last pulse of a 3T mark is delayed within a range of 0.4 through 2.8 nsec. than said termination timing. Here, T is the unit period. As such, the start timing and termination timing of a pulse are set depending on the unit period, but the amount of timing adjustment can be set to be an identical value independent of the change in unit period.
An information recording apparatus in accordance with a tenth invention is characterized by an apparatus of any one of the fourth to the ninth inventions, wherein said beam light controlling unit is further capable of controlling the beam light power and thereby modulates the power value for forming the record marks and spaces.
In the tenth invention, the beam light controlling unit can control the beam light power and thereby modulates the pulses for forming of record marks and spaces into four or five values. Accordingly, the shift quantity of record marks having different length is further reduced and the jitter is reduced.
Further, although the jitter tends to occur in a magnetic super-resolution medium on which record marks having a dimension smaller than the spot size of the beam light, the jitter can be reduced by adjusting the pulse timing when the predetermined permutational combinations of xe2x80x9cspace, record markxe2x80x9d is recorded, as described above.